The failure to detect, find and correct minor roof deterioration in the earliest stages is considered the greatest cause of premature roof failure. This is particularly true of roofing materials applied on low-slope or flat roofs. Costly roofing problems are often the result of design deficiencies or faulty application of the roof system. Even when properly designed and applied, all roofing materials deteriorate from exposure to the weather at rates determined largely by the kind of material and the conditions of exposure.
Several methods have been used to try and locate roof leaks after they have occurred. Electric capacitance meters identify leaks uses a low-frequency that measures dielectric constant changes in the roofing material as a result of moisture below the membrane. Infrared cameras allow technicians to scan roof surfaces for temperature differentials that signify moist areas through changes in thermal conductivity or evaporation. Electric field vector mapping uses a wire loop around the perimeter of the roof surface to introduce an electric potential between the structural deck and a selected roof area which is sprayed with water. The electric field potential caused by a conductive path to any roof membrane damage is then located using a sensitive voltmeter and a pair of probes.
All of the above methods are usually employed to assist in locating roof leaks after costly water damage has occurred.
U.S. Pat. No. 4,565,965 issued Jan. 21, 1986 to Geesen discloses an arrangement for detecting leaks in flat roofs covered with a gravel layer in which electrical pulses are transmitted through the moisture in the leak to the roof edge and then the roof is scanned by a pulse sensor to find the leak by locating the maximum amplitude.
Moisture detection sensors can also be placed under the roof membrane to detect the presence of moisture intrusion. However several roof designs incorporate membranes that are directly adhered to the roof deck thereby limiting the placement and effectiveness of this type of moisture sensor application.
In regard to pitched roofs which are of a different construction and hence provide different challenges and requirements, U.S. Pat. No. 5,081,422 issued Jan. 14, 1992 to Shih discloses an arrangement for detecting leaks in pitched roofs using parallel pairs of conductors to detect a change in resistance value therebetween caused by the presence of moisture where the pairs are arranged in an array of the pairs spaced in the x and y directions. Testing of each pair sequentially will locate the leak in the x and y direction. The pairs are typically located on the supporting plywood beneath the tar paper and shingles but can be located on top of the tar paper and underneath the shingles or tar/sand mixture. In all cases the conductors are provided in pairs at the same location in the roof construction.
In some cases the leakage current from roof drains, un-insulated metal flashings and other roof fixtures can result in higher than normal current leakage to grounding points on the roof membrane. While a guard circuit applied to adjacent grid conductors drains off most of the stray current, a small percentage of the current can leak past and reach the measuring conductor. This stray leakage current can be on the order of several milliamps and result in fault locating ambiguity in the area being tested.